imx6sx- M4 performance impacted during A9 wakeup time from sleep. What can be reason ?

[rakesh_patel]

Board

=======

imx6sx

Command used to put A9 in sleep:

==============

echo mem > /sys/power/state. 

A9 wake up once M4 send RPMSG.

Logs A9- Wakeup

====================

Freezing user space processes ... (elapsed 0.002 seconds) done.
Freezing remaining freezable tasks ... (elapsed 0.005 seconds) done.
Suspending console(s) (use no_console_suspend to debug)
PM: suspend of devices complete after 150.832 msecs
PM: late suspend of devices complete after 0.896 msecs
PM: noirq suspend of devices complete after 0.836 msecs
Disabling non-boot CPUs ...
In imx6q_pm_enter
M4 is busy, enter WAIT mode instead of STOP!
PM: noirq resume of devices complete after 0.406 msecs
PM: early resume of devices complete after 0.473 msecs
PM: resume of devices complete after 166.394 msecs
Restarting tasks ... done.

Issue

=======

M4 performance gets degraded in wakeup time = 166.394 msec(Sleep to wakeup time).  After 166msec, M4 performs as expected like wakeup.

What can be the reason here?

[rakesh_patel]

Note: Out application on the M4 side is using just some GPIO read/write and RAM write + rpmsg operations only.

[igorpadykov]

Hi rakesh_patel

I am afraid it is not possible to exclude some modules from the

suspend-resume flow. Probably one can disable them before entering low power

mode, then reenable again.

Best regards
igor

[rakesh_patel]

@igorpadykov : 

I found culprit module that affect M4 performance.

Module= mmc3:0001

I have bypassed(ignored) this module from device_pm_add API("drivers/base/power/main.c") then M4 application is working fine.

But, this is not ideal solution. I am not getting, why mmc3 is affecting M4 performance.

[igorpadykov]

Hi rakesh_patel

probably mmc3 is performing some operations during low power mode

sequence, what device is attached to mmc3 . One can try to tweak some dts settings:

 

Best regards
igor

[rakesh_patel]

@igorpadykov :

I tried the above-mentioned dts setting. But it is not working.

We are using "MTFC32GAPALBH" Emmc. 

[rakesh_patel]

@igorpadykov :

Any clue for why "mmc3:0001" is creating an issue with M4 performance?

We also have an EPIT timer in the M4 application which uses a peripheral clock. 

And as per the imx6sx reference manual,

=======

"Any change of the periph_clk_sel and periph2_clk_sel sync
mux select will involve handshake with the MMDC. Refer to
the CCDR and CDHIPR registers for the handshake bypass and
busy bits

"

I also bypassed the MMDC handshake. Still, M4 performance is impacted. 

Just for more information:

===========

Our M4 application uses the following things:

1) RPMSG

2) EPIT timer

3) read/write GPIO 

4) read and write RAM - physical memory 

[igorpadykov]

>Any clue for why "mmc3:0001" is creating an issue with M4 performance?

this may be due to handshake when changing certain root clock dividers that require
handshake, handshake with GPC during power-down and power-up sequencing
of individual subsystems.

Best regards
igor

[rakesh_patel]

@igorpadykov :

Any idea, how to debug out and fix this further?

[igorpadykov]

Hi rakesh_patel

for performance issues NXP has special service:

https://contact.nxp.com/new-prof-svcs-sw-tech

Suggest to proceed with it.

Best regards
igor

[rakesh_patel]

@igorpadykov :

Thanks a lot for giving pointers for the debugging.

But this issue is automatically resolved in the new BSP code.

[igorpadykov]

Hi rakesh_patel

from log: "PM: resume of devices complete after 166.394 msecs"

seems  166msec is necessary for processor to exit from low power mode:

restore pmic voltages, restart PLLs, details can be found in sect.19.5.3.3.2 Exiting STOP mode

i.MX 6SoloX Applications Processor Reference Manual

Best regards
igor

[rakesh_patel]

@igorpadykov :

I also believe the same. But my purpose is to exclude modules from the suspend-resume flow that affect M4 performance.

I have attached list of module using custom debugging prints(Please find attached)

Query:

1) Which modules affect M4 performance?

2) How to exclude those modules from suspend-resume?